Honestly, I have no projects or specific uses for these languages. Rather, I am treating it as a tool for learning and to experience low level programming.

I might make some kind of machine learning application in it later down the line though.

The usual recommendation "for learning and to experience low level programming" would be C. See this for example http://www.joelonsoftware.com/articles/CollegeAdvice.html although that was written before Go and Rust.

Also if you're mucking about with machine learning a lot of the libraries seem to be in C or C++. I played about a bit with computer vision using Python but sometimes the Python bindings don't work or don't exist and I was thinking it would be easier to just call the things from the C/C++ they are written in.

We're actually growing a rather nice machine learning ecosystem on the Rust side, though obviously it's much less mature than the C/C++ solutions. See https://github.com/autumnai/leaf/blob/063ce978004b8bf4b7fc74... for an example.

In that case, I would recommend Rust because it's just harder to learn than the other options.

C++ for fundamentals plus RAII?